The next generation systems achieving higher-speed and larger-capacity communications than the currently-operated 3rd generation and 3.5th generation cellular radio communication systems include LTE (Long Term Evolution) and LTE Advanced being an advanced version of LTE, which are standardized by the standardization organization 3GPP.
In the LTE system (including the LTE Advanced), a radio base station transmits downlink control information (DCI: Downlink Control Information) for controlling radio communications with a radio terminal by using a downlink control channel (PDCCH: Physical Downlink Control CHannel). There is an overlap in frequency band of the downlink control channel between radio base stations.
In the LTE Advanced, discussion is in progress on provision of a heterogeneous network in which there both exist a high-power base station (a so-called macrocell base station) and a low-power base station (a so-called picocell base station or a femtocell base station). The heterogeneous network can distribute a load of the high-power base station to the low-power base station.
In general, a radio terminal connects with a radio base station that provides a radio signal with the highest received power among multiple radio base stations. Thus, in the heterogeneous network, a radio terminal is less likely to connect with the low-power base station. Against these circumstances, there has been proposed a technique of expanding the self-coverage of a low-power base station by controlling a radio terminal so that the radio terminal will connect with the low-power base station even when the received power from the low-power base station is not the highest (see, for example, NON-PATENT DOCUMENT 1).